Note that this will work with any version of doit there is no need
to have any modification in doit internal code.

doit is a generic tool that aims to by different kinds of applications.
There is no one task definition interface that will make everyone happy.
doit provides the most basic and flexible one based on dicts...

I must agree that this decorator interface looks more readable :)
But it has many limitations and can be used only for trivial tasks.

Limitations:

only one action per task

no support for command line (shell) actions

not easy to create several tasks with same actions

You could go one step further and create a
custom task loader,
so you could get rid of the task_all.
I might add something like this for next doit release...